1. Field of the Invention
This invention relates in general to photography and in particular to photographic elements provided with a magnetic stripe that is useful for sound recording. More specifically, this invention relates to photographic elements having a magnetic recording stripe comprised of finely-divided magnetic particles dispersed in an alkali-insoluble, cross-linked polymeric matrix, to a process for the manufacture of the aforesaid elements, and to a coating composition for use in the manufacture of the aforesaid elements.
2. Description of the Prior Art
A well known method of applying a magnetic recording stripe to a photographic element is to apply the magnetic striping composition over the anti-halation layer which is present on the back side of the support, that is, on the side of the support opposite to the image-forming layers. However, the anti-halation layer is designed to be removed during processing of the element, and, accordingly, is comprised of a binder which is soluble in alkaline photographic processing solutions. Thus, if the magnetic stripe is applied over the anti-halation layer, it will be removed along with the anti-halation layer during processing unless suitable procedures are utilized to avoid such removal. Among the procedures which are known for this purpose is that of U.S. Pat. No. 3,220,843. As described in this patent, a magnetic stripe which is composite with the anti-halation layer and firmly adhered to the support so as to resist removal by alkaline photographic processing solutions can be formed by incorporating an N,N-dialkylamide in the magnetic striping composition. By use of the N,N-dialkylamide, the anti-halation layer is partially or completely dissolved in the region of the stripe and the striping composition is thereby able to reach the support and anchor thereto. A similar procedure is described in U.S. Pat. No. 3,647,541 in which the magnetic striping composition contains a combination of 2-methoxy ethanol and a dioxane. A different approach to the problem of applying a magnetic striping composition over an anti-halation layer is to incorporate in the magnetic striping composition an agent which is capable of reacting with the binder in the anti-halation layer to thereby insolubilize the anti-halation layer in the region of the stripe and prevent its removal in photographic processing solutions. This technique has been the subject of several patents, each of which relates to the use of particular insolubilizing agents; for example, the diazomethanes of U.S. Pat. No. 3,227,555, the compounds with reactive aldehyde groups of U.S. Pat. No. 3,840,374, the compounds having isocyanato or thioisocyanato groups of U.S. Pat. No. 3,870,525, the carbodiimides of U.S. Pat. No. 3,891,444, the m-benzene disulfofluorides of U.S. Pat. No. 3,999,992, and the combinations of bis-epoxides or polyepoxides with formamide or a sulfoxide of U.S. Pat. No. 4,008,088.
While the methods of the prior art are capable of providing a magnetic recording stripe which resists removal by alkaline photographic processing solutions to a fair degree, they suffer from significant disadvantages which restrict their usefulness. For example, the magnetic striping composition may require a lengthy drying period with the result that drying chambers must be of great length and, consequently, are very costly. Moreover, because of the long time and relatively high temperatures needed for drying, rehumidification chambers may be needed to replace moisture driven out of the photographic element during the drying operation. This adds greatly to the cost and complexity of the equipment. Also, in cases where a solvent incorporated in the striping composition is of high boiling point, the temperatures required to completely dry the stripe may be so high as to render it very difficult to avoid damage to the photographic element. Many other limitations also restrict the usefulness of the compositions and methods of the prior art. For example, the striping compositions are frequently lacking in adequate storage stability, incapable of adequately dispersing the magnetic particles, difficult to coat, or incapable of accepting a sufficiently high loading of magnetic particles with the result that the stripe is lacking in adequate frequency response and audio output. Moreover, the stripe often does not have adequate adhesion to the element and because of the difficulty in coating may lack the precise width and thickness characteristics necessary for optimum performance. The requirement of precise width and thickness is critical in the magnetic striping art. This is true both for the magnetic recording stripe and for the balance stripe which is located on the same side of the film as the recording stripe but adjacent to the opposite edge of the film, and is intended to provide for uniform stacking of the film convolutions as the film is wound on a core. Moreover, since these stripes must be very narrow--typically about 0.7 millimeters for the recording stripe and about 0.35 millimeters for the balance stripe on 8 millimeter motion picture film--it is apparent that the coating operation is a very difficult one and that the striping composition must meet very exacting requirements to enable it to be satisfactorily coated.
It is toward the objective of providing an improved composition and method for magnetic striping of photographic elements which overcomes many of the disadvantages and limitations of the prior art that the present invention is directed.